RESEARCH INTO THE DISTRIBUTION OF THE GENUS BATHYPOREIA
(CRUSTACEA, AMPHIPODA) BY MEANS OF MOLECULAR MARKERS
Demaerel Virginie, Steven Degraer, Magda Vincx and Thomas Remerie
Ghent University, Marine Biology Section, Krijgslaan 281-S8, 9000 Gent, Belgium
E-mail: virginie_demaerel@hotmail.com
The taxonomic identification of amphipods is complex and often a great expertise is
required to get to the right species identification (Costa et al., 2004). A lot of recent
studies, using molecular techniques, have highlighted that biodiversity can be strongly
underestimated when based only on morphological identification. Genetic study of
morphological identical species showed that these can be genetically very divergent,
which leads to the recognition of so-called cryptic species (Knowlton, 2000).
The present study focused on species of the genus Bathyporeia, which is one of the most
problematic taxa concerning species identification (d’Udekem d’Acoz, 2004). The
general objective of this study was to get insight in the degree of genetic structuring
between and within species of this amphipod genus. For this purpose, intertidal and
subtidal samples from the most common Bathyporeia species (B. pilosa, B. sarsi, B.
pelagica, B. elegans and B. guilliamsoniana) were collected along the French-BelgianDutch coast. These samples were analysed using DNA sequencing information from the
mitochondrial cytochrome oxydase I (COI) gene and the Internal Transcribed Spacer
(ITS) from ribosomal DNA.
Both molecular markers (COI and ITS) revealed a clear phylogenetic separation
between the five species. The evolutionary patterns within the genus could not be easily
resolved since the positions of the different clades were not supported by high bootstrap
values. The intraspecific diversity within B. guilliamsoniana appeared to be very high.
The phylogenetic analysis showed the presence of two distinct B. guilliamsoniana groups
supported by high bootstrap values. The degree of sequence divergence within this
species was also much higher compared to the other species, suggesting that both
distinct B. guilliamsoniana groups could be recognized as two subspecies or two
(cryptic) species.
In general, the intraspecific degree of haplotype diversity (h) tends to be higher for the
subtidal species (B. guilliamsoniana, B. elegans) than for the intertidal species (B. pilosa,
B. sarsi, B. pelagica). This might be linked to the higher stability of the subtidal habitat
of these species. For the intertidal species B. pilosa and B. sarsi, the genetic diversity in
the populations Cap Blanc Nez and De Panne was much lower compared to other
locations. For both locations, a significant negative Tajima’s D value was observed,
suggesting that a bottleneck or selective sweep could explain this lower diversity.
When comparing the degree of genetic diversity and structuring within both intertidal
species B. pilosa and B. sarsi, the latter seemed to be more diverse. Although only a
limited number of B. pilosa specimens were analysed, a significant geographic
structuring could be found between the populations of Cap Blanc Nez and De Panne.
In contrast, the analysis of the variation between B. sarsi populations showed a more
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moderate (non-significant) degree of genetic structuring. This could mean that in
general B. pilosa populations are more isolated than B. sarsi populations. A possible
explanation for this pattern could be found in the different zonation of both species on
the beach. B. pilosa occurs strictly on the highest part on the beach in a less wide zone
compared to B. sarsi, what means that during high tide they are less long under water
and hence get less time for horizontal dispersion.
References
Costa F.O., M.R. Cunha, T. Neuparth, C.W. Theodorakis, M.H. Costa and L.R. Shugart.
2004. Application of RAPD DNA fingerprinting in taxonomic identification of amphipods: a
case-study with Gammarus species (Crustacea: Amphipoda). Journal of the Marine
Biological Association of the UK 84:171-8.
D’udekem d’Acoz C. 2004. The genus Bathyporeia Lindström, 1855, in western Europe
(Crustacea: Amphipoda: Pontoporeiidae). Zoologische Verhandelingen.162p.
Knowlton N. 2000. Molecular genetic analyses of species boundaries in the sea. Hydrobiologia
420:73–90.
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